1. Field of the Invention
The present invention relates to an amorphous copolyester, and in particular relates to an amorphous copolyester with a wide range of glass transition temperatures.
2. Description of the Related Art
Heat-shrinkable films are widely used for labeling, protection, parceling, and wrapping of glass, metal, ceramic and plastic bottles, boxes, container, and pipes. For example, heat-shrinkable films may be used as labels on food and drugs and as labels on plastic containers such as soft drink bottles. In general, shrink films are classified into two categories: (1) biaxially oriented films for wrapping, wherein the film shrinks in both the x-and y-axis directions; and (2) uniaxially oriented films, wherein the film primarily shrinks in a stretched or oriented direction and has a little shrinkage in the non-stretched or non-oriented direction.
Although shrink films may be made of polystyrene (OPS), polyethylene, polypropylene, and polyesters, the common shrink film is made of polyvinylchloride (PVC). PVC has good heat-shrinkable properties, however PVC is not suitable for low temperature shrink packaging. Moreover, the incineration of PVC generates hydrogen chloride which causes corrosion of the incinerator and environmental pollution. In addition, the specific gravity of PVC and PET both are 1.33, and thus it is hard to separate the two materials. Therefore, amorphous copolyester has been developed to replace PVC.
At present, copolyester polymer (PETG), from the Eastman Kodak company, polymerized by 1,4-cyclohexanedimethanol monomer is the main amorphous copolyester used. However, this kind of amorphous copolyester cannot effectively shrink at higher temperatures. Therefore, an amorphous copolyester with a wide shrink temperature range is needed.